[PATCH 1/1] windowscodecs: Correct GIF LZW compression initialization for images with truncated color palette.

[Jiajin Cui]

From: Jiajin Cui <[e-mail]>

Supersedes https://gitlab.winehq.org/wine/wine/-/merge_requests/9486

Signed-off-by: Dmitry Timoshkov <[e-mail]>
---
 dlls/windowscodecs/gifformat.c | 37 ++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/dlls/windowscodecs/gifformat.c b/dlls/windowscodecs/gifformat.c
index 4fde4f81bba..290ae6bf899 100644
--- a/dlls/windowscodecs/gifformat.c
+++ b/dlls/windowscodecs/gifformat.c
@@ -1415,7 +1415,7 @@ static inline int read_byte(struct input_stream *in, unsigned char *byte)
     return 0;
 }
 
-static HRESULT gif_compress(IStream *out_stream, const BYTE *in_data, ULONG in_size)
+static HRESULT gif_compress(IStream *out_stream, const BYTE *in_data, ULONG in_size, int color_bits)
 {
     struct input_stream in;
     struct output_stream out;
@@ -1429,7 +1429,7 @@ static HRESULT gif_compress(IStream *out_stream, const BYTE *in_data, ULONG in_s
     out.gif_block.len = 0;
     out.out = out_stream;
 
-    init_code_bits = suffix = 8;
+    init_code_bits = suffix = max(2, color_bits);
     if (IStream_Write(out.out, &suffix, sizeof(suffix), NULL) != S_OK)
         return E_FAIL;
 
@@ -1534,6 +1534,7 @@ static HRESULT WINAPI GifFrameEncode_Commit(IWICBitmapFrameEncode *iface)
             if (hr == S_OK)
             {
                 struct image_descriptor imd;
+                int colors, color_bits = 1;
 
                 /* Image Descriptor */
                 imd.left = 0;
@@ -1548,23 +1549,33 @@ static HRESULT WINAPI GifFrameEncode_Commit(IWICBitmapFrameEncode *iface)
                 }
                 /* FIXME: interlace flag */
                 hr = IStream_Write(This->encoder->stream, &imd, sizeof(imd), NULL);
-                if (hr == S_OK && This->colors)
+                if (hr == S_OK)
                 {
-                    UINT i;
-
-                    /* Local Color Table */
-                    memset(gif_palette, 0, sizeof(gif_palette));
-                    for (i = 0; i < This->colors; i++)
+                    if (This->colors)
                     {
-                        gif_palette[i][0] = (This->palette[i] >> 16) & 0xff;
-                        gif_palette[i][1] = (This->palette[i] >> 8) & 0xff;
-                        gif_palette[i][2] = This->palette[i] & 0xff;
+                        UINT i;
+
+                        /* Local Color Table */
+                        memset(gif_palette, 0, sizeof(gif_palette));
+                        for (i = 0; i < This->colors; i++)
+                        {
+                            gif_palette[i][0] = (This->palette[i] >> 16) & 0xff;
+                            gif_palette[i][1] = (This->palette[i] >> 8) & 0xff;
+                            gif_palette[i][2] = This->palette[i] & 0xff;
+                        }
+                        hr = IStream_Write(This->encoder->stream, gif_palette, sizeof(gif_palette), NULL);
+                        if (hr == S_OK)
+                            colors = This->colors;
                     }
-                    hr = IStream_Write(This->encoder->stream, gif_palette, sizeof(gif_palette), NULL);
+                    else
+                        colors = This->encoder->colors;
+
                     if (hr == S_OK)
                     {
+                        while ((1 << color_bits) < colors) color_bits++;
+
                         /* Image Data */
-                        hr = gif_compress(This->encoder->stream, This->image_data, This->width * This->height);
+                        hr = gif_compress(This->encoder->stream, This->image_data, This->width * This->height, color_bits);
                         if (hr == S_OK)
                             This->committed = TRUE;
                     }
-- 
GitLab

https://gitlab.winehq.org/wine/wine/-/merge_requests/9923